As processes for producing diaryl oxalate, (1) a method in which oxalic acid and a phenol compound are directly esterified by heating them at 100 to 130.degree. C. in an organic solvent in the presence of a esterification catalyst, as disclosed in Japanese Examined Patent Publication No. 52-43,826; (2) a method in which a dialkyl oxalate is reacted with a diaryl carbonate, as disclosed in Japanese Examined Patent Publication No. 56-8,019 and Japanese Unexamined Patent Publication No. 49-42,621, and (3) a method in which a dialkyl oxalate is ester interchange-reacted with an aryl ester of a lower fatty acid, as disclosed in Japanese Examined Patent Publication No. 56-2,541 and No. 57-47,658 are known.
However, the method (1) in which oxalic acid and the phenol compound are directly esterified to produce a diaryl oxalate is disadvantageous that the reaction rate is extremely low and thus a long reaction time is necessary. Therefore the method (1) is not satisfactory from the viewpoint of industry. Also, the methods (2) and (3) in which a dialkyl oxalate is reacted with a diaryl carbonate or with an aryl ester of a lower fatty acid to produce an aryl oxalate, are not industrially satisfactory, because method (2) or (3) is disadvantageous in that the production of a starting compound consisting of the diaryl carbonate or aryl ester of lower fatty alcohol is difficult, and therefore the starting compound is expensive and difficult to obtain; and various by-products other than the target compound are produced in a large amount, and thus very complicated and troublesome refining process is necessary to isolate the diaryl oxalate.